"Hotter summers may not be as catastrophic for the Greenland ice sheet"

Meltwater stream flowing into a large moulin in the ablation zone (area below the equilibrium line) of the Greenland ice sheet. (Image courtesy Roger J. Braithwaite, The University of Manchester, UK via GISS)

‘Hidden plumbing’ helps slow Greenland ice flow

Hotter summers may not be as catastrophic for the Greenland ice sheet as previously feared and may actually slow down the flow of glaciers, according to new research.

A letter published in Nature on 27 January explains how increased melting in warmer years causes the internal drainage system of the ice sheet to ‘adapt’ and accommodate more melt-water, without speeding up the flow of ice toward the oceans. The findings have important implications for future assessments of global sea level rise.

The Greenland ice sheet covers roughly 80% of the surface of the island and contains enough water to raise sea levels by 7 metres if it were to melt completely. Rising temperatures in the Arctic in recent years have caused the ice sheet to shrink, prompting fears that it may be close to a ‘tipping point’ of no return.

Some of the ice loss has been attributed to the speed-up of glaciers due to increased surface melting. Each summer, warmer temperatures cause ice at the surface of the sheet to melt. This water then runs down a series of channels to the base of the glacier where it acts as a lubricant, allowing the ice sheet to flow rapidly across the bedrock toward the sea.

Summertime acceleration of ice flow has proved difficult for scientists to model, leading to uncertainties in projections of future sea level rise.

“It had been thought that more surface melting would cause the ice sheet to speed up and retreat faster, but our study suggests that the opposite could in fact be true,” said Professor Andrew Shepherd from the University of Leeds School of Earth and Environment, who led the study.

“If that’s the case, increases in surface melting expected over the 21st century may have no affect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”

The researchers used satellite observations of six landlocked glaciers in south-west Greenland, acquired by the European Space Agency, to study how ice flow develops in years of markedly different melting.

Although the initial speed-up of ice was similar in all years, slowdown occurred sooner in the warmest ones. The authors suggest that in these years the abundance of melt-water triggers an early switch in the plumbing at the base of the ice, causing a pressure drop that leads to reduced ice speeds.

This behaviour is similar to that of mountain glaciers, where the summertime speed-up of ice reduces once melt-water can drain efficiently.

###

Study co-author Dr Edward Hanna from the University of Sheffield added: “This work also underlines the usefulness of modern gridded climate datasets and melt-model simulations for exploring seasonal and year-to-year variations in Greenland ice sheet dynamics and their relationship with the global climate system.”

The study was funded by the Natural Environment Research Council’s National Centre for Earth Observation, the Philip Leverhulme Trust, and by the European Commission Ice2Sea project.

89 thoughts on “"Hotter summers may not be as catastrophic for the Greenland ice sheet"”

Well, that`s a cheerful bit of news.
As the props and supports drop away from from the catastrophists case, i can`t help but wonder, just how much time will pass before they, and the absurd edifice they have built collapses and vanishes up their own fundament.
Not soon enough i suspect.

The Greenland ice sheet covers roughly 80% of the surface of the island and contains enough water to raise sea levels by 7 metres if it were to melt completely.
+++++++++++++++++++++++++++++++++++++++++++++++++++
Hmm, 7 metres………that’s a lot!

The article implies a thirty percent reduction of the ice would increase global sea levels by about 2.3 metres.
1000 years ago there was a third less ice.
There was no perceptible rise in global sea levels.
This was during a time when human population was much lower and water use was lower too.
So if the ice melted by a third again when water use is an order of magnitude much higher today we should not see flooding.

Summer temperatures in Greenland have been relatively constant, varying between from + 5 to 7 degrees C) during last 100 years. It is the winters that got much warmer (from -9 to -5 C) consequently less ice generated.http://www.vukcevic.talktalk.net/LFC10.htm

Heat From Earth’s Magma Contributing To Melting Of Greenland Icehttp://www.sciencedaily.com/releases/2007/12/071212103004.htm
It’s an old article but, I think it is A contributing factor . . . .
It’s also why I think contributing scientists are important, . . . . they can at least warn you as when it might be a real good idea to “run like the devil himself is after you!”
And once again, it’s why I say . . . any and all knowledge can be used to abuse.

If the Greenland ice sheet melted every time the climate went through a warming cycle, historical records would show seacoast towns getting regularly submerged. But history shows an amazingly steady sea level. The article explains why:

“If that’s the case, increases in surface melting expected over the 21st century may have no effect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.” <– (warning: required grant trawling language added by authors)

“Summertime acceleration of ice flow has proved difficult for scientists to model, leading to uncertainties in projections of future sea level rise.”
Says everything you need to know about climate science in general. Models.
Do these people ever get out of the office these days and do real every day physical
science? Rubbish in, Rubbish out.

Oh I see. Instead of the glacier floating on a lubricating sheet of water, the increasing water flow as spring progresses cuts dendritic channels through the ice (and perhaps the basal rock rubble and dirt), re-grounding the glacier.
Yet glaciers still from time to time speed up. Seems like glaciologists have more basic research to do. Tying “global warming” to glacier research is just t0day’s hook to keep the research funding flowing.

Well when the floating arctic ice melts, it does expose sea water to the oblique radiation from the summer sun, which will allow solar energy to reach into the Artic Ocean depths and increase water temperatures (which often are warmer on the surface, having come from the tropics) But that should also allow for a significant increase in evaporation from those heated waters; which inevitably will lead to greater snow falls; and quite likely on the surrounding lands (there’s more land north of +60 deg, than there is water) And having all that snow and ice growing on the lands surrounding the arctic ocean, is likely to increase the earth albedo, more than is lost from the floating ice; those vast land areas see more sunlight than the Arctic ocean does.
So I wouldn’t be in any hurry to predict a snowballing loss of albedo, when the floating sea ice melts; all that open cold water will also take up more CO2 from the atmosphere.

It’s as if every week / month we find evidence of why there won’t be catastrophic positive feedback runaway global warming. And here I was being told about lubrication and tipping points. I’m beginning to warm to the Gaia hypothesis. ;O)

Nils-Axel Morner
“The Greenland Ice Cap did not melt during the postglacial hypsithermal (some 5000 to 8000 years ago), when temperature was about 2.5 C higher than today. Nor did it melt during the Last Interglacial when temperature was about 4C higher than today. As to time, it would take more than a millennium (with full thermal forcing) to melt the ice masses stored there.”http://climaterealists.com/?id=6137

Al Gore ……. says
——–
1000 years ago there was a third less ice.
There was no perceptible rise in global sea levels.
——–
What part of the law of conservation of mass and the concept of density don’t you understand?
Do this experiment. Fill a glass of water to the brim. Hold it over your lap. Drop in an ice cube. Predicted outcome: you wet your pants.

Al Gore’s Holy Hologram says:
January 26, 2011 at 12:44 pm
“The article implies a thirty percent reduction of the ice would increase global sea levels by about 2.3 metres.”
Very good. That means I can eat more beef!!!

Maybe what the Warmists are seeing is just part of a cycle. It’s been warmer before I think.

“We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.”
Takuro Kobashi et. al.http://www.springerlink.com/content/n567324n1n3321h3/

I was debating the Arctic Report Card (ARC) with a glaciologist from SkS last fall. He was pretty much pulling a chicken little by saying the sky was falling because the last 5 years were such absolute dramatic proof that the sky was falling based on the Surface Mass Balance.
So I ran an analysis using the actual numbers from the and the numbers in the report proved that nothing significant is happening. I did the same for another peer-reviewed journal article and found different numbers, but the same result.
All the studies show it has lost mass in the last 10 years, but they also show that there is nothing statistically unusual about the last 10 years.
My write-up over the debate is here:http://theinconvenientskeptic.com/2010/12/mass-accumulation-of-greenlands-ice-sheets/

Of course this quoted headline, “Hotter summers may not be as catastrophic for the Greenland ice sheet,” does not appear in the article. (The article is here: http://www.nature.com/nature/journal/v469/n7331/full/nature09740.html ; a sub. may be required.)
The issue is this. Glaciers are melting. As the melt water drains to the land/ice surface there is concern that this will lubricate the ice and enhance the sliding of the sea sheer toward to sea. This article claims to show (and the claim seem credible) that higher rates of melting can lead the melt water to carve out channels to the sea and because of these channels the friction between the ice and land can be higher than with low melting — but, I would add, certainly higher than with no melting! With higher temps the glaciers will melt and sea level will rise, but this work means the time it takes to rise the sea levels will be longer, although a lot more work needs to be done before good quantitative models can be constructed.REPLY: The quote is from the press release – Anthony

Won’t Greenland take nearly 10,000 years to completely melt at it’s current pace?
Not sure how that breaks down say in 200 year increments (sea rise vs melt) but I’m sure it’s slow enough that New York and other cities can deal with the problem at a much later date…

However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”
Lol. Mmmmmphh errrrrrr….. It doesn’t mean we admit to being wrong, or hyping disaster… It just means we might do so eventually. We still Get grants and publicity from hyping apocalypsis, so you should expect that to continue for some time…

So have they figured out that glaciers “retreat” when they shrink and “expand” when they are getting bigger? Or are they still on that pill about glaciers advancing into the sea is proof that they are getting smaller?

vukcevic says:
January 26, 2011 at 12:45 pm
“…It is the winters that got much warmer (from -9 to -5 C) consequently less ice generated.”
I would have thought a slightly ‘warmer’ air over Greenland would hold more moisture. Even so, -5 is still below freezing. Greenland is probably the largest highest feature within the Arctic and at it’s highest point is over 3000m. You will know that with either a dry or wet lapse rate temperatures over Greenland can only be lower than what they are at sea level, and at the top that can be between -18 to -30 below the -5, or whatever the temperature is at sea level. As Greenland sticks up so much it will squeeze moisture out of whatever air that passes over it.
Anthony visited this subject back in 2009:http://wattsupwiththat.com/2009/08/27/why-the-greenland-and-antarctic-ice-sheets-are-not-collapsing/
“In reality the Greenland and Antarctic ice sheets occupy deep basins, and cannot slide down a plane. Furthermore glacial flow depends on stress (including the important yield stress) as well as temperature, and much of the ice sheets are well below melting point.”
At least the Nature acknowledges observation instead of ignoring it.

Surely a glacier’s flow depends on it’s weight, not temperature. If a glacier gains mass higher up this could increase it’s speed. So a rise in temperature could speed up a glacier as it gains mass but also shorten it as the freezing point moves up in height.

According to the mann made climate hippies Greenland has been through worse warm weather before, and the damn ice is still frakking there a t’ousand years later.
And before that there were several periods with several hundred years of warmer ‘an normal weather incapsulating that enormously thickly icy island.
Apparently, nobody seem to really know how the ice works in and for Greenland, because physically it would have made more sense if inner siberia and inner US/Canada was covered in a couple of mile high ice sheet instead of Greenland which has always be wrapped in kind of warm water.
And more ‘an a hundred t’ousand years o’ accumulated pesky soot has still to make a significant melting dent. :p
So, essentially, Greenland is in a state of abnormal flux then compared to the climate hippies standards of normal.
Besides nobody knows what the actual proper size of Greenland used to be before satellites.
Come to think of it, but what is the supposed normal size of Greenland’s ice sheet?

Well at least there is acknowledgement that a glacier is not just a big slab of ice. It has a complex internal hydraulic system that we still know very little about. We shouldn’t make assertions about what glaciers will do until we learn a lot more about them.

DD More says: Since the ice has been there for 420,000 years
Well, that is true for Antarctica, but not for Greenland. The ice cores show quite clearly that there is almost no ice during the glacial maxima and a lot during the warm periods. To be clear, many mountains in Greenland were above the ice pack 30k years ago, but are currently way under the top of the ice today. As suggested above, warm weather produces more snow, cold weather produces more sublimation (less ice).

“Do this experiment. Fill a glass of water to the brim. Hold it over your lap. Drop in an ice cube. Predicted outcome: you wet your pants.”
An idiotic simplistic example that does not even begin to have real world parallels (changes in water use, coastal and water table absorption, land use changes, plate tectonics and continental drift, sea depth changes, anthropogenic and natural terraforming, precipitation changes, vegetation changes, etc).
The world is not a glass of water waiting for an ice cube to be dropped into it.

Isn’t this the himalayas furore all over again? A quick look at Wikipedia (yes, I know …!) gives the mean altitude of the icesheet at 2,135 metres, so its surface is about 1 mile high on average. It’s rather cooler up there than at sea level, and a slightly warmer ocean nearby will increase the hydrological cycle to give more precipitation….
The icesheet isn’t about to melt any time soon. It will take several millenia – if we are not already back in an ice age by then.

@JimG on doing the math:
Yeah, I just did a back of the envelope calculation. Using the IPCC’s figure of 2.85e6 km**3 for the ice sheet and Wikipedia’s figure of 3.6e8 km**2 for the area of the oceans, you get 2850000 km**3/360000000 km**2 = 0.00792 km, or 7.92 m sea level rise.
This doesn’t take into account a lot of other factors, but it’s ballpark figure. At least the alarmists can do their math, even if they sometime apply it strangely.

I took a look at Colorado’s Jason data – Seasonal Signal Removed, Inverse Barometer Applied
Its interesting to look at the last few years at the same point
2006.7236 26.640
2007.7280 25.493
2008.7054 23.759
2009.7370 31.748
2010.7415 28.119
A 4 year net of 1.5mm
I really wonder where this claim of dangerous sea level rise came from?

Enjoy your blog. Jaw open after finding this article today and coming here to watch you all discuss it.
But, pardon my undergraduate ignorance, are they trying to tell us that somehow we just didn’t take into account the known phenomenon of water-carved riverways under the ice?
Didn’t the Grand Canyon get carved by a river and it’s supposed to be some kind of revelation that this event, on something as soft as a little frozen water with a nice dandy island sitting under it, wouldn’t be happening? And that it might serve as a “wick” of the heat that supposedly would melt the ice sheet otherwise?
Look! A satellite photo! Newly discovered river under the ice! That doesn’t mean global warming isn’t happening though.
Thank you all.

…Study co-author Dr Edward Hanna from the University of Sheffield added: “This work also underlines the usefulness of modern gridded climate datasets and melt-model simulations for exploring seasonal and year-to-year variations in Greenland ice sheet dynamics and their relationship with the global climate system.”…
Hmmm…..gridded…is that where they interpolate values where no data exists?
Modern…. does that mean, erm, adjusted, enhanced?
simulations…. what’s wrong with observation and review/documentation/research
of existing data?

To Jim G – by the way, a ball-park calculation would go: volume of the icesheet is 2,850,000 cubic km (683,750 cu mi). When melted this gives approx 91% of its volume as water, so 2,593,500 cu km.
The earths mean radius is, say, 6,370 km so its surface area (= 4*pi*r^2) is 509,905,000 sq km. About 71% of that is ocean, which is 356,933,500 sq km.
Ocean levels will therefore rise by 2,593,500 / 356,933,500 km, which is 7.27 metres.
It’s about right.

I was under the impression that the ‘arctic’ winters were due to the moving Jet stream and blocking ‘high’ phenomenon as described by some guy from the Metoffice on that TV prog (Britains Big Freeze I think it was called) the other week.
Having said that, it is quite feasible that the Daily Mail reporters know more about the weather/climate than the MetOffice these days – LOL!

Jim G says:
January 26, 2011 at 2:43 pm
Can’t believe that the Greenland ice melting would raise sea levels that much. Anyone done the math on that? Such a small patch, such a big ocean.
========================================================
lol, yeh, my calcs were just like JamesS’. (I didn’t bother with the density thing, either.) Of course, this implies some implausible assumptions. For instance, would all of the water really run off to the oceans? No. They’d have rivers and lakes and the like. Then, of course, the question would be would atmospheric H2O increase? I say probably, but others may disagree. Also, the extra liquid H2O would somehow understand a boundary line between rivers and lakes, and seas and oceans. So, we’d only see an increase of rain in the oceans.

1DandyTroll says:
January 26, 2011 at 2:42 pm
. . . physically it would have made more sense if inner siberia and inner US/Canada was covered in a couple of mile high ice sheet…
Glacial ice is much like a sedimentary rock – both require a source of sediment and have to be deposited for the mass to form. Grains of sand can be deposited when carried by moving water that slows. Grains of ice can be deposited when carried by air masses. So without an appropriately moist air mass to provide a source for the material needed for the deposit, it is highly unlikely that the mass will grow.
The mountains of B.C. and Washington State have high snow levels as they receive moist air masses from the Pacific Ocean –air high in moisture. Greenland likewise has moist-air mass source regions nearby. The regions mentioned by you in the quote above do not. Those areas also warm considerable in summer and are low in elevation. Case closed.
Antarctica is quite dry in places but high and cold. With so little melt, slow deposition is plenty good enough.
An afterthought: Some of these issues are best looked at on a globe and not a flat map.

There may be some debate as to the global extent of the MWP but what we know as an incontrovertible fact is that at that time Greenland was considerably warmer than today (witness Viking settlements that are beginning to reveal themselves as the ice retreats and at those settlements the Vikings were able to farm – today it is presently too cold to farm there) and we know that even further back in time, Greenland was weven warmer. The world did not come to an end because of these warmer temperatures affecting Greenland nor were there drastic sea level rises. This sis a fact which strongly undermines the alarmists scare stories. The nub of this matter is as Jimbo states:
Jimbo says:
January 26, 2011 at 1:26 pm
It’s as if every week / month we find evidence of why there won’t be catastrophic positive feedback runaway global warming. And here I was being told about lubrication and tipping points. I’m beginning to warm to the Gaia hypothesis. ;O)
Nils-Axel Morner
“The Greenland Ice Cap did not melt during the postglacial hypsithermal (some 5000 to 8000 years ago), when temperature was about 2.5 C higher than today. Nor did it melt during the Last Interglacial when temperature was about 4C higher than today. As to time, it would take more than a millennium (with full thermal forcing) to melt the ice masses stored there.”http://climaterealists.com/?id=6137http://dx.doi.org/10.1016/0033-5894(74)90038-6

I could be totally wrong, but I seem to remember that when the IPCC (make sign of cross, grasp rosary beads) made predictions on sea-level rise for this century, they actually didn’t include glaciers flowing into the sea, because they (rightly) concluded that they couldn’t model it accurately? That is, they were cautious and prescient.
Anyway, nice post, and interesting research.

History of Greenland:http://en.wikipedia.org/wiki/File:Grtemp.png
I believe the recent readjustments of ice loss are based on new gps data at the base of the ice which allowed accurate maping of the isostatic rebound of the rock below the ice. What I thought was interesting is that it appeared to show that the rock below the deepest part of Greenland was sinking under the weight of the ice instead of rebounding. In otherwords gaining volume.

richard verney says:
January 26, 2011 at 4:31 pm
“(witness Viking settlements that are beginning to reveal themselves as the ice retreats and at those settlements the Vikings were able to farm – today it is presently too cold to farm there) ”
Hi there richard. Your statement that it is too cold to farm in Greenland today is wrong.
I think you’ll be interested in these links that show there are plenty of farms in Greenland today.http://www.environmentalgraffiti.com/ecology/greenland-is-green-again/392
“51 farms (all of them sheep farms except for one with 22 cows)
[snip]
A local supermarket in Greenland is stocking fresh locally grown cauliflower, broccoli, and cabbage for the first time.”
And another interesting article on farming in Greenland…http://www.spiegel.de/international/spiegel/0,1518,434356,00.html
Global Warming a Boon for Greenland’s Farmers
“Known for its massive ice sheets, Greenland is feeling the effects of global warming as rising temperatures have expanded the island’s growing season and crops are flourishing. For the first time in hundreds of years, it has become possible to raise cattle and start dairy farms.”
Many people think that Greenland is completely covered in ice. Do a quick Google search for images of Greenland farms or take a tour of South West Greenland in Google Earth if you need more proof that there is plenty of green[farm]land in Greenland today.
Regards, Martin

Regarding the ‘melt and rising sea level’ discussion. Do the doomsday scenario’s take into account that a lot of the water is already below sea level? ( in some places almost 1,000 feet below sea level)
The two James’ did some quick calculations in this thread…did you guys account for this when you estimated the sea level rise. When the ‘Greenland is melting’ argument gets trotted out by Algore and other alarmists I would assume they have some research that has calculated the rise in sea level….is it safe to assume they properly accounted the sub sea level ice? Or did it take an armchair scientist like me to figure it out?

I think this is an interesting and important article. It shows that scientists who develop results which show that climate change may not be catastrophic are willing and able to get their results published.
This indicates that charges, made by some, that there is a conspiracy at work, to promote alarmism, and scientists that don’t conform lose funding and are discouraged from publishing, have no real basis.
As a previous poster said, the IPCC did not include accelerated melting of the Greenland Ice sheet in its sea level estimate, because the process was insufficiently understood, and the data was not there. This vindicates the collective judgment of the scientists who were responsible for the sea level rise projections made by the IPCC.
It will be interesting to see the followup papers on this subject. The paper does not mean that the world’s glaciers are not losing ice, because they are melting. It only means that the speed with which they are sliding into the ocean is not increasing due to lubrication by melt water. There is still acceleration as a result of the breakup of ice shelves which serve to hold back the glaciers from sliding into the ocean. The paper doesn’t deal with this phenomenon at all.http://www.scientificamerican.com/article.cfm?id=polar-ice-shelf-break
“In Greenland the story of not so glacial changes in the outlet glaciers is much the same. Their seaward edges are speeding up, and the ice sheet behind them is thinning. Measurements of local gravitational anomalies by the GRACE satellites show that the Greenland ice sheet, particularly in its southern reaches, is rapidly losing mass. “The ice sheet is on a diet,” Bell says. A lot of Greenland ice is slipping into the Atlantic Ocean.”
The observations in the above paper apply to specific glaciers. The experience of other researchers on other glaciers appears to be different.http://www.truth-out.org/article/greenlands-ice-sheet-is-slip-sliding-away
“The camp has been rafting on the ice stream toward the sea, on average, at about 1 foot every day. Since Steffen pitched the main tents, the camp has moved about a mile downhill.
When Zwally started tracking the velocity of the ice with Global Positioning System sensors in 1996, the ice flow maintained a steady pace all year.
But he soon discovered that the ice around Swiss Camp had abruptly shifted gears in the summer, moving faster when the surface ice started to melt. By 1999, the ice stream had almost tripled its speed to about 3 feet a day.
In an influential paper published in Science, Zwally surmised that the ice sheets had accelerated in response to warmer temperatures, as summer meltwater lubricated the base of the ice sheet and allowed it to slide faster toward the sea.”

Malcolm Latarche says:
January 26, 2011 at 2:53 pm
“And it looks as though the glaciers are growing in the Himalayashttp://www.sciencenews.org/view/generic/id/69058/title/Glaciers_largely_stable_in_one_range_of_Himalayas ”
I think you are not reading carefully and allowing an anti AGW bias to blind you to the facts. The lead in the article says,
“Glaciers largely stable in one range of Himalayas
Ice in Karakoram region may even be growing, thanks to debris cover.”
So it is not established that the glaciers in the Karakoram region are growing, it says they are stable and may be growing. In fact, the article says that most of the glaciers studied are shrinking and the Karakoram region is an exception.
“Throughout most Himalayan ranges, roughly 65 percent of the studied glaciers were shrinking, Dirk Scherler of the University of Potsdam, Germany, and his colleagues report in the January 23 Nature Geoscience. But in Karakoram, 58 percent of studied glaciers were stable or slowly expanding up to 12 meters per year.”

John Brookes if the scientist had taken andrew comment into account then this research paper would not have made it here. Scienctist do not take all things into account because they will not allow debate so they do not get other ideas to check out, hence papers like these come up and show us they do not take any and all things into acoount. John you will find even more scienctist here than at Jonovas, so do not try your trolling arguments here they will shred you.

@Andrew: while accepted that much of the base of the Antarctic sheet is below sea level, is this also true of Greenland (the one discussed here)? Could you provide a link to some data on this please – I will then come back with revised estimate (ball-park, as earlier!).

It just makes such a mockery of the catastrophism we have had rammed down our throats for the last 15 years. And in the soul searching whch is now beginning about why nobody listens to scientists anymore, I am afraid that they have absolutely no one but themselves to blame.

If there is water enough in Greenland to mathematically raise the levels of the oceans by close to 8 meters, if it melted, such a happening would mean that surface of the oceans would increase enormously through the no doubt immense flooding. The net increase in ocean level I leave to someone else to calculate…

LazyTeenager says:What part of the law of conservation of mass and concept of density don’t you understand?
Do this experiment. Fill a glass of water to the brim. Hold it over your lap. Drop in an ice cube. Predicted outcome: you wet your pants.
Fill a glass of water to the brim. Hold it over your lap. Drop in anything else. Predicted outcome: you wet your pants.
Fill a glass about half way, drop in an ice cube and mark the level of water on the side of the glass. Wait for the ice to melt. Is the level of water higher, lower, or the same as the mark you have made?
Ice melting from a land mass – how heavy is the ice before it melts? Does that unmelted ice have any significant effect on the level of the land beneath it? For broad comparison purposes there is historic data on Britain from the end of the last glaciation which had ice around a mile/mile and half deep at Birmingham, in this glaciation it didn’t reach all the way South. Scotland and the islands in the North initially rebounded fairly quickly from being released from the ice, some 150 ft in places iirc; it’s still going on but at a slower rate, Southhampton on the South coast is still sinking. You might be able to find enough data from geologists’ sources on-line to work out what effect this would have on Greenland. Let us know when you do.

It is my understanding of Greenland that the ice sheet sits in a depression caused by the weight of the ice and it is this that prevents ice from ‘speeding up’ towards the sea. Ice in contact with the surface rock melts due to the weight of ice above and warming from geothermal heat. There must be sub-icesheet lakes on Greenland due to this as there are on Antarctica.

Robert Clemenzi says:
January 26, 2011 at 2:44 pm
DD More says: Since the ice has been there for 420,000 years
Well, that is true for Antarctica, but not for Greenland. The ice cores show quite clearly that there is almost no ice during the glacial maxima and a lot during the warm periods. To be clear, many mountains in Greenland were above the ice pack 30k years ago, but are currently way under the top of the ice today. As suggested above, warm weather produces more snow, cold weather produces more sublimation (less ice).

The ice cores most definitely do not show this. The Greenland ice extends to the edge of the continental shelf during glaciations and is much larger than during interglacials. It is the accumulation that is smaller since climate is much drier but this is more than balanced by less melting.

<blockquote<Does that unmelted ice have any significant effect on the level of the land beneath it?
It sure has. In central Sweden the land has risen about 300 meters since the ice melted 10,000 years ago, and that is without counting the rise that occurred while the ice was thinning but had not yet melted completely. The total rise was probably closer to a kilometer. At the same time areas outside the icecap (e. g. southern England, Netherlands, northern Germany) are sinking as material flows slowly back into the depression under the former icecap.

I suspect that many catastrophists within the climate science community have had second thoughts and are beginning to explore ways in which they can retain their credibility, their funding and their careers as they slowly and carefully retreat from their previous extreme Chicken Little positions. It takes a lot of courage to hold one’s hand up to getting day-to-day stuff wrong, but when a professional lifetime is invested in what is becoming evident was an error, the amount of courage required for such admissions must be enormous.
Some scientists obviously don’t have that courage, as witness Trenberth’s ridiculous demand that the null hypothesis be reversed.

@Dan: good point, but if the sea level rise were to inundate an additional 1% of the earth’s surface area (5E+6 sq km – a lot of land, but possible) this would reduce the rise from 7.27 to 7.16 m on my ball-park figures, to give some idea of scale.
@Andrew: and if it first had to back-fill a pond of 1.71E+5 sq km area (the full sheet) x 0.5 km deep, say, the rise would then be only 4.80 m.

TimC says:
January 26, 2011 at 10:09 pm
@Andrew: while accepted that much of the base of the Antarctic sheet is below sea level, is this also true of Greenland (the one discussed here)? Could you provide a link to some data on this please – I will then come back with revised estimate (ball-park, as earlier!).

While the Greenland icecap is situated in a depression surrounded by highlands or mountains (which is the reason it is so extremely stable) relatively little of it is based below sea level. If it melted completely central Greenland would becom a large rather shallow freshwater lake draining westwards. There is good map on page 10 of this:http://www.geus.dk/publications/bull/nr14/nr14_p01-13_A1b.pdf

Peter says:
January 26, 2011 at 12:42 pm
Be prepared for a whole raft of such, “it might not be as bad as we thought” reports over the next few years.
It’s a face-saving exercise.

That is probably quite true, but I think we should be open to consider an alternative:
As the CAGW bunch looses its grip, dissenting views are easier to publish. This is not new, there were always critical views of catastrophic hypothesis, but they became more silent during the political dominance of climate science. See for example an excelent article about the stability of Antarctica during the last 14 million years by D. Sugden and its relation to how hypothesis work in earth sciences:The East Antarctic Ice Sheet: unstable ice or unstable ideas?

To add to my previous comment, this paper from some of the same authors stresses the uncertainty of the models regarding the Greenland Ice Sheet. The degree of uncertainty makes any prediction basically useless, but we have hardly heard anything about those results, even if the paper is from 2007:Impact of model physics on estimating the surface mass balance of the Greenland ice sheet
Abstract:Long-term predictions of sea level rise from increased Greenland ice sheet melting have been derived using Positive Degree Day models only. It is, however, unknown precisely what uncertainties are associated with applying this simple surface melt parameterization for future climate. We compare the behavior of a Positive Degree Day and Energy Balance/Snowpack model for estimating the surface mass balance of the Greenland ice sheet under a warming climate. Both models were first tuned to give similar values for present-day mass balance using 10 years of ERA-40 climatology and were then run for 300 years, forced with the output of a GCM in which atmospheric CO2 increased to 4 times preindustrial levels. Results indicate that the Positive Degree Day model is more sensitive to climate warming than the Energy Balance model, generating annual runoff rates almost twice as large for a fixed ice sheet geometry. Roughly half of this difference was due to differences in the volume of melt generated and half was due to differences in refreezing rates in the snowpack. Our results indicate that the modeled snowpack properties evolve on a multidecadal timescale to changing climate, with a potentially large impact on the mass balance of the ice sheet; an evolution that was absent from the Positive Degree Day model.

It is interesting how a couple folks have commented on this quote…
“If that’s the case, increases in surface melting expected over the 21st century may have no affect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”
And added in the notion that the authors are “grant trawling” since they mention ocean-driven melting. With no evidence to counter the authors’ statement, the commenters here resort to accusations. Way to go, very classy.

tty says:
January 27, 2011 at 3:15 am
“While the Greenland icecap is situated in a depression surrounded by highlands or mountains (which is the reason it is so extremely stable) relatively little of it is based below sea level. If it melted completely central Greenland would becom a large rather shallow freshwater lake draining westwards. ”
Are you sure? The map seems to indicate several depressions below sea level, the largest about 500km wide by 750 km long. There are large parts that are between 100m – 200m below sea level with the deepest between 200m and 300m. Not as low as the Dead Sea but considerably larger in area. It would make it a bigger area below sea level than the Caspian sea. Were you being sarcastic?

@tty: thanks – very informative. On the hat-throw basis before, I eyeball the residual lake as about 1/3rd total Greenland land area and, say, 250m mean depth so 142,500 cu km volume. Allowing for that, sea level rise would be 6.77m – but this would effectively be at 0C temperature and there would be extra thermal expansion at lower latitudes.
I think it all points to 7m being about the correct figure.

Does the calculated increase in sea level take into account the fact that the sea/land boundary is not generally vertical, so as sea levels rise, the area of ocean over which the calculation is based, actually increases significantly. If the area increases, the resultant rise, for a given volume of additional water, must be less.
It is nowhere near a linear relationship

@Dan: the rise will only affect the oceans and the newly inundated littoral areas, not the entire globe.
@Tony B: as the rise was only reduced by 11cm, allowing for immediate inundation of all the littoral areas in full, this didn’t seem to matter much. Perhaps halve the difference, as a reasonable estimate?

TimC,
My calculation lays out a 5.8 m layer of water across the entire globe. If only some parts are flooded, the rise will be greater and approach the 7.something figure.
This means that, contrary to my first posting, there is little alleviation from ocean area increase. Bugger.

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